The present invention relates to a sheet-like object convey apparatus for a sheet-fed rotary printing press, which grips the end of a sheet-like object fed from the upstream side of the convey direction and conveys it to an impression cylinder.
Generally, in a sheet convey apparatus of this type, sheets stacked on a feed unit are attached by the suction port of a sucker unit one by one, are fed onto a feeder board by rotation of a feed roller, and are conveyed on the feeder board toward a feedboard by a feed tape or the like. The sheets fed onto the feedboard are jogged at their leading ends by a register, and are gripped by the grippers of a swing. The gripped sheet is conveyed to the impression cylinder of a printing press by the swing motion of the swing pivotally supported by a swing shaft, and is then gripped by the grippers of the impression cylinder.
In the sheet convey apparatus of this type, the trailing side of the sheet expands or shrinks in the right-to-left direction (a direction perpendicular to the sheet convey direction) by a high pressure and a water content supplied when the sheet is subjected to printing. When the sheet expands or shrinks, printing registration called fan-out registration of the sheet on the trailing edge for multi-color printing causes misregistration, leading to defective printing. This problem is solved in Japanese Patent Laid-Open No. 7-52361.
The sheet convey apparatus described in this reference has a rod, a slide member, and a cam plate. The rod is axially slidable, supported in a swing shaft. The slide member moves together with the rod and has a cam follower. The cam plate is fixed to a gripper pad and has a tapered cam surface. The cam follower comes into contact with the cam plate. In this arrangement, when the swing shaft swings, the rod reciprocally moves in the axial direction accordingly, and the slide member also reciprocally moves in the axial direction. Then, the cam follower slides on the cam surface of the cam plate, and grippers which grip a sheet, and a gripper shaft supporting the gripper pad are deflected in the sheet convey direction.
In this state, when the sheet is transferred to the grippers of the cylinder and the gripper pad is restored to the straight state, the two ends of the sheet are pulled by the grippers at the two ends so that the trailing end of the sheet is stretched taut. As a result, even if the trailing side of the sheet expands or shrinks in the right-to-left direction, the trailing end of the sheet is stretched taut until the sheet is gripped by the cylinder. Therefore, the expansion and shrink of the sheet are corrected, so that the fan-out registration is corrected.
In the sheet-like object convey apparatus for the conventional sheet-fed rotary printing press described above, while the rod moves in the axial direction, the cam follower brought into tight contact with the cam surface of the cam plate rolls on the cam surface and does not come into slidable contact with it. At the right and left moving ends of the rod, however, the cam follower is in slidable contact with the cam surface. More specifically, at the right and left moving ends of the rod where the moving direction of the cam follower changes, the rod is temporarily stopped, and movement of the cam follower is stopped accordingly. Since a rolling inertia acts on the cam follower, the cam follower is temporarily rotated in the rolling direction while it is stopped. As a result, the surface of the cam follower is brought into slidable contact with the cam surface.
In this case, the cam surface with which the cam follower comes into slidable contact has a certain length with respect to the moving length in the right-to-left direction of the rod which deflects the gripper pad. For example, when the moving length of the rod is several mm, the length of the slidable contact of the cam surface is in units of mm. In addition, in the conventional sheet-like object convey apparatus for the sheet-fed rotary printing press described above, since the cam follower is urged against the cam surface of the cam plate with a high pressure due to linear contact, a load is concentrated on that portion of the cam follower which is urged by the cam surface. While the load is concentrated on the cam surface and part of the cam follower in this manner, the cam follower comes into slidable contact with the cam surface. Hence, the cam surface and part of the cam follower tend to wear easily, posing a problem on durability.